Procedure to increase position location availability

ABSTRACT

A device, method and system are provide which permits the methodology used to make the position determination to change dynamically in connection with achieving a position fix of a desired accuracy.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/563,037, filed Jul. 31, 2012, entitled “PROCEDURE TOINCREASE POSITION LOCATION AVAILABILITY”, which is itself a continuationof U.S. patent application Ser. No. 13/223,193, filed Aug. 31, 2011,entitled “PROCEDURE TO INCREASE POSITION LOCATION AVAILABILITY”, whichis itself a continuation of U.S. patent application Ser. No. 10/935,785,filed Sep. 7, 2004, entitled “PROCEDURE TO INCREASE POSITION LOCATIONAVAILABILITY”, each of which are assigned to the assignee hereof andincorporated herein by reference.

BACKGROUND

The ability to locate persons, vehicles, and the like has become moreimportant in recent years, particularly in view of new technologiesbeing introduced and increasing concerns over safety and security. Aperson or vehicle can be located by determining the location of a mobileradio device carried by the person or vehicle. For example, it isdesirable to provide a cellular telephone system with the ability todetermine the geographic location of an individual cell phone used toreport an emergency so that such location can be reported to emergencyresponse workers such as police, fire and ambulance services.

Several schemes for determining one's position on Earth are available.One way to determine position involves the use of the global positioningsystem (GPS). The GPS was originally conceived and developed by the U.S.Department of Defense as a military navigation system. Over time,elements of the system have become increasingly available for civilianuse. The GPS uses a constellation of 24 satellites, in a geo-stationaryorbit, whereby position can be determined by timing satellite signaljourneys from a GPS satellite to a GPS receiver. Five spare orbitingsatellites are provided primarily for backup in case one of the 24satellites fail. The satellites transmit spread-spectrum signals on twofrequency bands L1 (1575.42 MHz) and L2 (1223.6 MHz). The signals aremodulated by two pseudo-random noise codes; a coarse/acquisition (C/A)code and a precision (P) code. The C/A code in the L1 band is the codepertinent to civilian applications. Additionally, the GPS signal ismodulated with a data message commonly referred to as the GPS navigationmessage.

Typically, a GPS receiver employs a trilateration scheme in an effort toobtain a position fix. For instance, a GPS-derived position can beaccomplished using two-dimensional trilateration. For example, signalsfrom three satellites can be used to determine position based on theintersection of three intersecting circles. More specifically, eachsatellite signal can provide a radius in which the GPS receiver can lie.Two intersecting radii allow the position determination to be narrowedto the area of intersection. Another satellite signal can provide athird radius indicative of the position of the GPS receiver since allthree radii should intersect at a single point. Expanding the forgoingconcept to three-dimensional trilateration, each satellite signal can beused to indicate a sphere whereby three intersecting spheres can used todetermine position which includes altitude information. More satellitesignals can be used, and typically are used to improve accuracy.

At the GPS receiver, the satellite signal is demodulated after it ismatched and synchronized with a pseudo-random noise code. The GPSreceiver uses the GPS navigation message to calculate satellite signaltransit times in addition to the coordinates of the GPS satellite.Position measurement by a GPS receiver can typically be accomplishedwithin 15 meters (50 feet). However, the accuracy of these calculationsare dependent upon measurement accuracy and satellite configuration.Atmospheric conditions can cause ionospheric delays. Additionally,uncertainties in satellite orbits can contribute to errors since,axiomatically, satellite orbits degrade over time. Reliance uponposition indication using GPS data can be additionally problematic inview of public safety concerns in today's environment.

In order to address signal availability problems associated with theGPS, server-assisted GPS was introduced in the late 1990s. Stationaryserver computers are provided with a stationary GPS receiver forreceiving GPS satellite signals. The stationary GPS receivers areassociated with an antenna having a full view of the sky in order toallow continuous monitoring of the signals from all visible GPSsatellites. A radio interface is provided with each server to allowcommunication with mobile GPS stations. In connection with a positionquery about a mobile GPS unit's position, the server transmits its GPSsatellite information, obtained from its stationary GPS receiver, to themobile GPS unit. This information includes a list of observable GPSsatellites and data which allow the mobile GPS receiver to synchronizeand match psuedo-random noise codes with those codes of the GPSsatellites. The mobile GPS receiver transmits its collected GPS data tothe server. The server, in turn, computes the position of the mobile GPSreceiver from the data provided by the mobile GPS and the stationaryGPS. While this scheme permits greater accuracy over non server-assistedGPS, satellite signal availability can still cause problems in acquiringan accurate position.

The enhanced signal strength (ESS) system employs a position locationscheme which is independent of the GPS. Three-dimensional informationcovering the terrain including buildings, structures and otherobstructions is collected in order to model radio frequency signalpropagation characteristics for a wireless transmitting antenna in agiven geographic area of interest. The results of the modeling arestored in a database. The position of a mobile locator is determined inconnection with the locator measuring the signal strength of a signalfrom a number of wireless transmitters. The position is calculated bythe system using input information from the mobile locator and thestored database information. This system has been used in Japan inconnection with the Personal Handy Phone System (PHS).

Other schemes for determining position, without using the GPS, make useof either the angle of arrival (AOA)of signals at receivers or the timedifference of arrival (TDOA) of signals at receivers.

The network-based angle of arrival scheme determines the location of amobile station (as, for example, a mobile phone, a personal digitalassistant with wireless communications capability, a portable computerwith wireless communications capability, a pager or other personalcommunications device) by determining the angle from which a signal isarriving at two or more fixed antenna sites. For instance, signaldirection or angle of arrival at each site can be determined from thedifference in time of arrival of incoming signals at different elementsof a single fixed antenna at that site. For instance, a two elementphased array antenna can be used to cover angles between 60° and −60°. Asix element phased array antenna, which is equivalent to three antennaswith 2 pairs of elements, can cover 360°. Equipment within thecommunication network combines the angle data from multiple sites todetermine the location of the mobile station. Proper angle measurementand the geometric relationship between the mobile station and fixedantennas can affect position measurement. Proximity of the mobilestation to the mid point between two fixed antennas can causesignificant position measurement error. For this reason, it is desirableto use three or more antenna sites in making AOA measurements.

The time difference of arrival scheme of determining position is anothernetwork-based solution which measures the time difference of arrival ofa radio signal to at least two antenna sites. Using the speed of anelectromagnetic wave and known transmit and receive times, the distancebetween a fixed antenna and mobile station can be determined Theprocessed information is translated into longitude and latitude positionreadings. The accuracy of synchronized clocking information necessary toproperly compute TDOA is critical to proper position measurement.Synchronized accurate clocking can sometime be problematic in TDOAmeasurement. TDOA position measurements can suffer as a consequencethereof. A mere micro second clocking error can contribute to severalmeters of error in position measurement.

Forward link trilateration can also be employed to determine positionwhereby the time difference of signal arrival from a base stationantenna to a mobile station can be calculated by measuring the phasedifference between pseudo-random noise coded signals being transmittedfrom at least two antennas to the mobile station. This scheme isparticularly useful for code division multiple access (CDMA) systems.Advanced forward link trilateration (AFLT) is a variation of this schemewherein the mobile station and base stations reverse roles. In AFLT, theposition of the mobile station is fixed in connection with the basestations receiving transmissions from the mobile station. In AFLT, themobile station measures CDMA phase offsets of different pilot phasenoises and reports them to the position determination entity at thenetwork. The position determination entity uses the different pilotphase measurements to perform forward link trilateration to compute theposition fix for the reporting entity.

Fingerprinting provides another approach to determining the position ofa mobile station. Radio frequency signal characteristics associated withvarious regions in a signal transmission area are collected in adatabase. Each grouping of signal characteristics for a region is knownas a fingerprint. The position of a mobile station is determined bycomparing an RF data sample collected by the mobile station tofingerprint data in the database. The comparison can be made at themobile station or at the server holding the fingerprint data. Thefingerprint data collected benefits from the collection of multi-pathsignals which arise through indirect signal paths from transmitter toreceiver. While not subject to many of the problems associated withother position identifying technologies, fingerprinting requiressubstantial work in data collection and is therefore economicallyfeasible only for highly populated, highly concentrated metropolitanareas.

Thus, as described above, numerous individual position-determiningschemes are known in the art. These schemes can be categorized broadlyas mobile station assisted modes (MS-Assisted mode) and mobile stationbased/standalone mode (MS-Based/Standalone modes). In the MS-Assistedmode, the position of the mobile station is determined by the by acomputer commonly referred to as the Network/position DeterminationEntity (PDE), which computer is connected to the communications network.The PDE can employ one of the methodologies outlined above as, forexample, TDOA, AOA, ESS, etc. In MS-Based/Standalone mode, the mobilestation computes its own position location using its processor usingdata available at the mobile station. One example of anMS-Based/Standalone system is a system in which the mobile station isequipped with GPS receiving and processing capability, and determinesits position based on GPS signals received at the mobile station.Individual scheme of position determination depends upon differentelements/resources which are susceptible to different types of errors.For instance, network connection is needed in all GPS MS-Assistedmethods regardless of the scheme (GPS, GPS plus AFLT, etc.) chosen. Evenif the GPS measurements are excellent, the MS-Assisted method is goingto fail if the network connection fails. Therefore in this instance, astand-alone GPS methodology would provide a better location estimate.

Each of the foregoing schemes for determining position may be inaccurateor unavailable on occasion as noted above. Thus, a mobile station ornetwork using any of these known position-determining schemes may failto obtain any result when asked to determine the current position of themobile station or may obtain an inaccurate result. A need thereforeexists to create a method for more reliably determining the position ofa mobile station with greater confidence.

SUMMARY

One aspect disclosed provides a method of determining the location of amobile device. A method according to this aspect includes determiningthe position of the mobile station using a first scheme of positiondetermination and, if the first scheme does not yield an acceptableposition result, repeating the determining using at least one furtherscheme of position determination different from the first scheme in atleast some repetitions until (i) a repetition returns an acceptableposition result or (ii) all available position-determining schemes havebeen used. The different schemes used in the method may use measurementsof different signals or different measurements of signal characteristicsas the basis for the position result. It is unlikely that all of thesedifferent schemes will fail to return an acceptable position result;thus, the reliability of the system is improved. In effect, the methodselects a position-determining scheme which gives acceptable resultsunder the prevailing conditions. The system switches schemes dynamicallyas conditions require.

A further aspect provides a method of determining the position of amobile station including making position determinations for the mobilestation, according to a plurality of different schemes, and determiningan estimate of error for each position determination scheme. The methodaccording to this aspect may include the further choosing one positiondetermination method having a smallest estimate of error, and selectingas the position of the mobile station a position result provided by thechosen position determination. This method effectively selects aposition-determining scheme which gives the best available results underprevailing conditions, so that here again the system switches schemesdynamically to meet changing conditions. Alternatively, the methodaccording to this aspect may include calculating the position of saidmobile station by combining a plurality of the position results as, forexample, by computing a weighted average of the position results.

A further aspect provides a mobile device and systems for locating amobile device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of one embodiment of a system.

FIG. 2 is a flow chart depicting a method of making positiondeterminations.

FIG. 3 is a flow chart depicting a method of making positiondeterminations.

FIG. 4 is a flow chart depicting a method of making positiondeterminations.

FIG. 5 illustrates a block diagram of interaction of a mobile stationwith a Position Determination Entity (PDE).

DETAILED DESCRIPTION

FIG. 1 illustrates, in functional block diagram form, a system includinga mobile station 2 and communications network 20 and associated positiondetermining entity (PDE) 14.

Mobile station 2 includes a processor 6, memory 8, and transceiver(transmitter/receiver) 10. As used herein, the term “transceiver” refersto any assemblage of components which will perform transmitting andreceiving functions. Thus, transceiver 10 may include common componentsused in both functions or entirely separate components for performingtransmitting and receiving functions. Transceiver 10 is capable oftransmitting and receiving signals appropriate for communication withnetwork 20.

The transceiver is connected to processor 6 so that the processor cancontrol the operations of the transceiver and so that the processor cansend data to the communications network 20, and receive data from thecommunications network, via the transceiver. The mobile station 2typically also includes components (not shown) for user communicationand user control. For example, where the mobile station is a cell phone,the mobile station will include a conventional microphone and speakerlinked to the transceiver under the control of the processor, and aconventional keypad and display (not shown) for entering and displayingdata. In the particular embodiment depicted, transceiver 10 is capableof receiving global positioning system (GPS) signals, and processor 6 iscapable of deriving a position result based on the GPS signals, usingsoftware stored in memory 8. Processor 6 is also arranged to determine aparameter associated with the expected error in the position result as,for example, the number of satellite signals received and used inarriving at such result.

Network 20 includes a plurality of base stations, such as cell phonetowers 22, 24, 26 and 28 at diverse locations. Each base stationincludes equipment 30 for monitoring signal characteristics orbroadcasting a signal of pre-selected characteristics as required in atleast one individual position-determining scheme. For example, the basestations may be configured to operate in an angle of arrival determiningscheme, in which case equipment 30 at each base station would include aphased-array antenna at each station and a circuit capable of measuringthe difference in time of arrival at the different elements.

Alternatively or additionally, the base stations may be arranged tooperate in a time of arrival monitoring scheme, in which case theequipment 30 at each base station would include conventional devices formonitoring the time of arrival of a signal at the station using anetwork-wide master clock or a local clock synchronized with such anetwork-wide master clock, so that the times of arrival determined ateach station can be compared with the time of arrival determined atevery other station.

The equipment 30 at each base station may also include equipment formeasuring signal parameters associated with the suitability of thesignals for use in a position-determining scheme. For example, theequipment 30 used in a time-of-arrival or angle-of-arrival scheme mayinclude equipment for measuring the strength of the received signals.

The position determining entity (PDE) 14 includes one or more computerprocessors 36 connected to base stations 22,24,26,28, and a memory 38connected to these processors. The memory 36 holds software whichinstructs the processor 36 to perform the functions required to derive aposition result for each individual position measuring schemeimplemented in the network components. For example, where the networkimplements a time-of-arrival scheme, the memory may contain datarepresenting the physical locations of the base stations andinstructions for calculating a position result in a conventional mannerbased on the differences in time of arrival at the various base stationsand the locations of the base stations.

As further explained below in connection with FIGS. 2-4, the PDEprocessor 36 also performs the functions of determining position basedon selection of one position result determined by one positiondetermining scheme from a plurality of results derived using differentschemes or based on a combination of such plural results. The element ofthe processor which performs these functions, referred to herein as acontroller, is shown as a separate functional element at 40.

This portion of the processor may include the same physical structuresas are used for other functions, or may include separate physicalstructures. The controller operates according to instructions and datastored in memory 38. Also, the processor 36 and memory 38 may bephysically dispersed. For example, memory 38 may be linked to theprocessor through communications network 20 or through another public orprivate network (not shown) as, for example, through the internet. Theelements of the processor also may be physically dispersed and linked inany suitable manner.

FIG. 2 illustrates a flowchart depicting a method of making positiondeterminations, using a system as discussed above with reference toFIG. 1. The method begins (step 100) when PDE 14 receives a request todetermine the position of mobile station 2. Such a request may be inputas a user command at the mobile station, or may be initiated by anothersource. For example, where the system is a cellular telephone systemlinked to a public safety answering point (PSAP) the request may comefrom the PSAP or may be initiated automatically whenever the mobilestation is in communication with the PSAP as, for example, when themobile station user dials “911” in the United States.

The PDE sends a command to the base stations, mobile station or both tocollect data and derive a position result according to a first positiondetermination scheme. (step 102) The position result returned by thefirst scheme is then tested for acceptability (step 104) according toone or more predetermined criteria. For example, where the first schemeis conventional GPS location, the PDE may command the processor 6 ofmobile station 2 to attempt to derive the position of the mobile stationbased on GPS signals received at the mobile station, and to communicatethe derived position result to PDE 14 through network 20 along with dataindicative of the quality of the result, such as data indicating thenumber of satellite signals received and used in deriving the result.

The PDE may apply an acceptance criterion based on the number ofsatellite signals used in deriving the result. For example, thecriterion may specify that a result derived using four or more satellitesignals is acceptable, whereas a position result derived using threesatellite signals is not acceptable, and that a position resultindicating that no position could be determined is also not acceptable.

In another scenario, a user may be lost and may locate himself/herselfby invoking position determination wherein processor 6 usesMS-Based/Standalone GPS methodology. However, due to signalunavailability or a weak GPS signal, the MS-Based/Standalone method mayfail. Mobile station 2 can direct processor 6 to use a method which usesAFLT measurements in addition to GPS measurements, i.e. a MS-Assistedmode, to increase the probability of obtaining a position fix.

Alternatively or additionally, a direct estimate of error may beincluded in the position result. For example, a position result may beexpressed in terms of latitude and longitude together with an accuracyindication or error estimate of plus or minus a number of feet ormeters. In the case of a GPS result using more satellite signals thanthe minimum required to derive a position result, the processor of themobile unit or the PDE may obtain an estimate of error by comparing theposition results derived from various subsets of the available satellitesignals.

The criteria for acceptability may include an acceptable tolerance was±75 feet, in which case a returned result accompanied by an estimate oferror of ±50 feet, would be found acceptable since it is within thetolerance of ±75 feet whereas a position result accompanied by an errorestimate of ±75 feet would be found to be unacceptable.

Yet another criterion which may be applied is comparison withpreviously-determined position of the mobile station. Memory 38 can holdhistorical positioning data representing a previously-determinedposition of mobile unit 2 and the time of such previous determination.The acceptance criteria may include a criterion such that a positionresult differing from a previously-determined position greater than athreshold limit per unit time since the last determination is regardedas unacceptable.

For instance, if a position result returned by the GPS scheme shows aground-based mobile station at a position 10 miles from a positiondetermined 2 seconds previously, such result may be deemed unacceptable.In a variant of this approach position determinations taken closelytogether may be averaged together so to calculate a moving average orcompared with one another to establish an average velocity of the mobilestation.

Any or all of the foregoing criteria, and other criteria, may be appliedin step 104.

If the position result returned by the first scheme is acceptable, thePDE 14 selects that result and as the position of the mobile station(step 106). The accepted result is communicated by the PDE to the mobilestation, to a PSAP or to any other appropriate destination as theposition determined by the method, and the method terminates. Thedetermined position may be expressed in the form of latitude andlongitude, or converted to a street address or map grid location or anyother suitable form.

However, if the position result returned by the first scheme is notacceptable, then the method branches to step 108. In this step, the PDE14 commands the base stations and/or the mobile unit to perform a secondposition-determining scheme different from the firstposition-determining scheme.

For example, if the first position-determining scheme used GPS, thesecond position-determining scheme may use time difference of arrival.The times of signal arrival at the various base stations 22,24,26,28 aredetermined and communicated to PDE 14, which calculates a positionresult unit based on these time differences. Here again, the informationreported to PDE 14 or compiled at PDE 14 may include data about thesignal measurements used to derive the position result, such as thenumber of base stations receiving the signal, the strength of thesignals received at the various base stations and the like, andoptionally may also include a direct estimate of the error in theposition result. Here again, the controller compares the position resultwith acceptance criteria and determines whether the position resultreturned by the second scheme is acceptable (step 110).

The criteria applied in this step may include some or all of the samecriteria as discussed above in connection with step 104, or may includevariations of these. For example, in a time difference of arrivalscheme, acceptance criteria may include a requirement for receipt of thesignal with a certain minimum signal strength at least 3 base stations.If the position result returned by the second position-determiningscheme is acceptable, the controller 40 selects that position result asthe position determined by the method and communicates that position(step 112) in the same manner as discussed above in connection with step106.

If the position result returned by the second scheme is not acceptable,the process continues using further repetitions of the position-derivingstep using further different schemes for deriving position results (step114), and further determinations of acceptability (step 116) until anacceptable position result is found and communicated (step 118) in thesame manner as discussed above or until all of the n positiondetermining schemes possible using the equipment included in the systemhas been used. If the nth scheme is completed without returning anacceptable positioning result, the controller 40 returns an errormessage (step 120) and the method ends.

In a variant, the order in which the method uses different schemes maybe adjusted based on the results achieved. If a particular scheme isfound to give acceptable results in the sequence of steps discussedabove, that scheme may be placed first in the order of use. Thus, whenanother position request is received by PDE 14, and the sequence ofsteps discussed above is initiated again, that scheme will be used inthe first position-determining step. It is likely that such scheme willgive acceptable results. By using a previously-successful scheme as thefirst scheme, the system minimizes the number of times it must “hunt”through a plurality of schemes before finding an acceptable scheme.

In a variant, the method may begin again (return to step 102) insteadof, or in addition to, returning the error message. In a furthervariant, in the event that all n methods have been used without findingan acceptable position result, the system may select the best positionresult from among the available results. For example, where all of theposition results are accompanied by data representing an estimate oferror, the system may choose the position result associated with thesmallest estimate of error and communicate that result.

In a method according to another embodiment, the controller 40 actuatesthe components of the system to perform all N position-determiningschemes in parallel and selects one position result from among theposition results returned. FIG. 3 illustrates a flowchart depicting thismethod.

Position determinations according to n schemes are carried out inparallel (steps 202, 204, 206). Each position result is tested againstpre-selected acceptability criteria as discussed above (steps 208,210,212) and unacceptable results are discarded. Acceptable results arecompared (step 214), and the best result is selected according to apredetermined measure of merit (step 216). For example, where theresults are accompanied by estimates of error, the result associatedwith the lowest estimated error is selected.

Alternatively, the controller may assign an estimate of error or otherfigure of merit to each result based upon a known or assumedrelationship between conditions associated with such result and theaccuracy of the result. For example, the controller may assign a morefavorable figure of merit (such as a low estimate of error) to a resultderived from angle of arrival at four base stations and a less favorablefigure of merit (such as a high estimate of error) to an angle ofarrival result based on signals received at three base stations. Theselected position result is communicated as the position determined bythe method (step 220).

In a variant of this method, the step of determining acceptability ofeach result and discarding unacceptable results (steps 208-212) areomitted, and all results are passed to the comparison step withestimates of error or other figures of merit.

In a method according to another embodiment, (FIG. 4) plural positionresults are obtained using different position-determining schemes (steps302-306), and an estimate of error or other figure of merit isdetermined for each result in the manner discussed above (steps308-312). Each position result is considered a random variable with astated measure of confidence embodied in the estimate of error (accuracyestimates) or other figure of merit. The various results are combined(step 314) with one another to yield a combined result using a combiningalgorithm which gives different weights to the various individualresults according to this measure of confidence.

In one such combining algorithm, an average, weighted according to thelevel of confidence, is calculated for these position random variables.If, for example, n (n being an integer) readings were taken by ndifferent schemes, w₁, w₂, . . . , w_(n) represent the weighting factorsattributed to each position result and x₁, x₂, . . . , x_(n) representposition result, the weighted average can be expressed as follows:w₁x₁+w₂x₂+w₃x₃/(w₁+w₂+w₃).

In order to accord a greater weight to a position measurement with ahigh indication of accuracy, (and conversely accord the measures withthe least confidence a smaller weight) the reciprocals of the accuracyindications can be used as weighting factors in calculation of aweighted average. Consequently, should x₁ have an accuracy of ±5 feet,x₂ have an accuracy of ±50 feet and x₃ have an accuracy of ±10 feet,weighting factors w₁, w₂, and w₃ would have values of 0.2, 0.02, and0.1, respectively. The x₁ reading is given the greatest amount of weightfollowed by x₂ and x₃ readings. The weighting factors can be calculatedusing other methods. For instance, the squares of the reciprocal of theaccuracy indication can be used for the weighting factors.

In yet another embodiment, the foregoing described position locationmethodology can be implemented by a mobile station and/or by theNetwork/PDE in conjunction with the mobile station.

FIG. 5 illustrates a block diagram of the interaction of mobile station2 with Network/PDE 14. Mobile station 2 includes position determinationmode multiplexer 4, processor 6, memory 8, transceiver(transmitter/receiver) 10 and display 11. In one aspect, mobile station2 will attempt to determine its position, within a pre-specifiedtolerance, using a Network/PDE method as directed by processor 6. Shouldthe position determination not achieve the pre-specified tolerance thenmultiplexer 4 dynamically switches modes in an effort to obtain aposition fix, of suitable accuracy, using another position determinationmethod.

The position location mode selected by switch 4 can employ a methodologybased in the mobile station 2, i.e., MS-Based/Standalone mode (e.g.,GPS) or a methodology based in the MS-Assisted mode using transceiver 10to communicate with network/PDE 14. Double arrow 12 signifies theinteraction of the network/PDE with mobile station 2 for the MS-Assistedmode of operation. In connection with a position being determined formobile station 2, in one embodiment of the invention, the location canbe shown on display 11 of mobile station 2. Alternatively, the positioncan be forwarded and/or determined at network/PDE 14.

Memory 8 can hold historical positioning data. Processor 6 is programmedto direct the operation of multiplexer 4. In conjunction with thestorage of previous mobile station location readings in memory 8, shouldthe current position readings change above a threshold limit, within apredetermined time period, such may indicate a significant error inposition measurement. Processor 6 can provide a response necessitatingthe determination of the mobile station position by another method. Forinstance, after 2 seconds, should the mobile station move 10 miles, thisdetermination is likely erroneous especially where mobile station 2 isground based. Alternatively, memory 8 can allow position determinationstaken closely together in time to be averaged together so as tocalculate a moving average. Although this provides a smoothing effectregarding changes in position over time, this method can introduce someerror. For some applications of position determination, this error maybe acceptable.

Mobile station position determination can be accomplished by choosingdifferent methods wherein each method comprises one or more schemes. Forinstance a GPS MS-Assisted method can comprise GPS or GPS combined withAFLT. A network-based method can comprise TDCOA or AOA or a combinationof both, while a GPS MS-Based/Standalone method may use, for instance,GPS only.

Conventional attempts at making mobile station position determinationsfail entirely if for some reason the particular position determinationmethod fails. Mobile station position determination according to theinvention permits methodologies which contain different positiondetermination schemes different from or in addition to a particularscheme that for some reason may fail to determine the position of themobile station.

Availability of a successful position determination scheme therebyincreases using the invention as compared with conventional methods.Further, the invention permits the use of different resources forposition determination, using the same scheme, from that which wouldotherwise fail using another resource.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the particular principles and applications.For example, the particular position-determining schemes referred to inconnection with FIGS. 1-4 are merely illustrative; any of the numerousknown individual position-determining schemes can be used. For example,trilateration schemes in which use time of arrival of signals frommultiple base stations can be used. Desirably, the variousposition-determining schemes rely, in whole or in part, on differentphysical measurements of signal characteristics, different signals, orboth. Also, the functions performed by the PDE 36 and controller 40 inthe examples discussed above can be performed in whole or in part byelements of the mobile station 2. Stated another way, the processor 6 ofthe mobile station can include functional elements which perform thefunctions of the controller 40. Also, the position-determining methodcan be performed to determine the positions of multiple mobile stationssimultaneously or sequentially. The techniques described herein can beimplemented in essentially any network, such as not only CDMA systemsbut also in time division multiple access (TDMA) systems or frequencydivision multiple access systems (FDMA) or space division multipleaccess (SDMA) systems. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A method of obtaining a position of a mobile station comprising: (a) determining the position of the mobile station using a first scheme of position determination, wherein the first scheme of position determination is based upon GPS, trilateration, server assisted GPS, cell identification, enhanced signal strength, angle of arrival, forward link trilateration, advanced forward link trilateration, fingerprinting or a combination thereof; and (b) if the determining does not yield an acceptable position result, repeating said determining using at least one further scheme of position determination different from said first scheme in at least one repetition until (i) a repetition returns an acceptable position result or (ii) a threshold number of available position-determining schemes have been used.
 2. The method of claim 1, wherein the at least one further scheme of position determination includes three or more schemes in addition to the first scheme of position determination.
 3. The method of claim 1, wherein the at least one further scheme of position determination is based upon GPS, trilateration, server assisted GPS, cell identification, enhanced signal strength, angle of arrival, time difference of arrival, forward link trilateration, advanced forward link trilateration, fingerprinting or a combination thereof.
 4. The method of claim 1, wherein the first scheme of position determination or the at least one further scheme of position determination includes a cell identification scheme, and wherein the cell identification scheme is based upon measurements of wireless communication signals by the mobile station, wherein the measured wireless communication signals identify cells from which the measured wireless communication signals are transmitted.
 5. The method of claim 4, wherein the wireless communication signals correspond to pilot signals.
 6. The method of claim 4, wherein the cell identification scheme corresponds to an advanced forward link trilateration scheme.
 7. The method of claim 1, wherein the first scheme of position determination or the at least one further scheme of position determination includes an enhanced signal strength scheme, and wherein the enhanced signal strength scheme is based upon transmissions from a plurality of terrestrial wireless transmitters.
 8. The method of claim 7, wherein the plurality of terrestrial wireless transmitters correspond to base stations.
 9. The method of claim 1, wherein the first scheme of position determination or the at least one further scheme of position determination includes a fingerprinting scheme, and wherein the fingerprinting scheme is based upon radio frequency (RF) data that is transmitted by a set of transmitters and measured at the mobile station.
 10. The method of claim 9, wherein the RF data includes multi-path signals that result from indirect paths between the mobile station and the set of transmitters.
 11. The method of claim 9, wherein the set of transmitters corresponds to a set of base stations.
 12. An apparatus configured to obtain a position of a mobile station comprising: means for determining the position of the mobile station using a first scheme of position determination, wherein the first scheme of position determination is based upon GPS, trilateration, server assisted GPS, cell identification, enhanced signal strength, angle of arrival, forward link trilateration, advanced forward link trilateration, fingerprinting or a combination thereof; and means for repeating said determination if the determination does not yield an acceptable position result using at least one further scheme of position determination different from said first scheme in at least one repetition until (i) a repetition returns an acceptable position result or (ii) a threshold number of available position-determining schemes have been used.
 13. The apparatus of claim 12, wherein the at least one further scheme of position determination includes three or more schemes in addition to the first scheme of position determination.
 14. The apparatus of claim 12, wherein the at least one further scheme of position determination is based upon GPS, trilateration, server assisted GPS, cell identification, enhanced signal strength, angle of arrival, time difference of arrival, forward link trilateration, advanced forward link trilateration, fingerprinting or a combination thereof.
 15. An apparatus configured to obtain a position of a mobile station comprising: a processor configured to: determine the position of the mobile station using a first scheme of position determination, wherein the first scheme of position determination is based upon GPS, trilateration, server assisted GPS, cell identification, enhanced signal strength, angle of arrival, forward link trilateration, advanced forward link trilateration, fingerprinting or a combination thereof; and repeat said determination if the determination does not yield an acceptable position result using at least one further scheme of position determination different from said first scheme in at least one repetition until (i) a repetition returns an acceptable position result or (ii) a threshold number of available position-determining schemes have been used.
 16. The apparatus of claim 15, wherein the at least one further scheme of position determination includes three or more schemes in addition to the first scheme of position determination.
 17. The apparatus of claim 15, wherein the at least one further scheme of position determination is based upon GPS, trilateration, server assisted GPS, cell identification, enhanced signal strength, angle of arrival, time difference of arrival, forward link trilateration, advanced forward link trilateration, fingerprinting or a combination thereof.
 18. A non-transitory computer-readable medium containing instructions stored thereon, which, when executed by an apparatus configured to obtain a position of a mobile station, cause the apparatus to perform operations, the instructions comprising: at least one instruction to determine the position of the mobile station using a first scheme of position determination, wherein the first scheme of position determination is based upon GPS, trilateration, server assisted GPS, cell identification, enhanced signal strength, angle of arrival, forward link trilateration, advanced forward link trilateration, fingerprinting or a combination thereof; and at least one instruction to repeat said determination if the determination does not yield an acceptable position result using at least one further scheme of position determination different from said first scheme in at least one repetition until (i) a repetition returns an acceptable position result or (ii) a threshold number of available position-determining schemes have been used.
 19. The non-transitory computer-readable medium of claim 18, wherein the at least one further scheme of position determination includes three or more schemes in addition to the first scheme of position determination.
 20. The non-transitory computer-readable medium of claim 18, wherein the at least one further scheme of position determination is based upon GPS, trilateration, server assisted GPS, cell identification, enhanced signal strength, angle of arrival, time difference of arrival, forward link trilateration, advanced forward link trilateration, fingerprinting or a combination thereof. 